Rudders are generally of framework and sheet
metal construction and therefore they have to be checked for corrosion,
wear and cracks. The rudder wear down is a measured to indicate excessive
wear in the steering gear system particularly the rudder carrier. The
significance of this is that for ram systems excessive wear can lead to
bending moments on the rams. The readings taken are offered for recording
by the classification society.

Trammel
This takes the form of an 'L' shape bar of suitable construction. When
the vessel is built a distinct centre punch mark is placed onto the ruder
stock and onto a suitable location on the vessels structure, here given
as a girder which is typical. The trammel is manufactured to suit these
marks As the carrier wears the upper pointer will fall below the centre
punch mark by an amount equal to the wear down.

Rudder clearance
Pads are welded to the hull and rudder. A clearance is given ( sometimes
referred to as the jumping clearance). As the carrier wears this clearance
will increase.

Process of removing a rudder (step by step):

The access panels in the rudder are cut out after the ship is in dry dock.
The rudder is held in place with chain falls and the rudder stock is then
removed along with the mechanical connections inside the ship. The rudder
stock is then lifted out through holes in the ships decks. The rudder
is then lowered and tilted until the pintle pin is free of its bearing
surface in the rudder horn. The rudder is then removed and set up vertically
in a work bay. The pintle pin nut access panel is removed and the pintle
pin nut is removed. The pintle pin is then removed. Usually the pintle
pin is very loose in the pintle pin bore and that is usually the reason
the rudder is being removed. Clearances of up to 1/4 inch have been found
where metal-to-metal interference fit should exist.

Shown below are some drawings indicating the components and the step by
step process of disassembling of the rudder: